Fireflies taste bad; birds and mice know this, and on a textbook level biologists do, too. That tantalizing, glowing taillight might as well be flashing, “don’t eat me.”
But Marc Branham inadvertently learned that lesson firsthand. Prospecting for fireflies one summer evening in graduate school, and having only two hands, he oh so gently tucked a specimen between his lips for safekeeping as he opened a collection jar.
The firefly did what any firefly would do; it released lucibufagin, a bitter defensive chemical. Branham, the unintentional predator, spit it out.
Now a University of Florida associate professor of entomology and one of the world’s foremost experts on fireflies, Branham can vouch for fireflies’ defense system.
“I haven’t done that again,” he says, recalling numb lips.
The pretty lights in the night know how to survive. Firefly light — bioluminescence — is a survival trait on two fronts, not only keeping fireflies from being eaten but also helping them find mates. Branham works to unravel the evolutionary journey of bioluminescence in fireflies, inspecting fossils and looking for forks in the family tree. How did bioluminescence develop, and why?
A career in insect systematics and behavior has decoded the mysteries, some at least, of the flashing beetles in the Mason jar at his bedside in childhood. But rather than dampen his enthusiasm, science has stoked it.
“If you just look at the fireflies in your back yard you only get one piece of the puzzle, but as you put it all together it’s amazing; it’s really fun how it builds this larger picture of the evolution of a communication system,” he says, voice rising, “and they use lights!”
In this language of light, fireflies send messages, a warning signal to a predator, a come-hither to a potential mate. It is a language that has inspired poetry and song.
Fireflies’ photic organs — those lovely beacons on their tails — use almost 100 percent of their energy to produce a cold light. By contrast, an incandescent bulb loses 90 percent of its energy to heat. Light organs can maximize this light by using a reflective layer, similar to the reflective material behind an automobile headlight.
The light is called bioluminescence, and it is generated by luciferin, luciferase and the chemical ATP, adenosine triphosphate. Luciferin, the protein, is activated by the enzyme luciferase, which draws energy for the chemical reaction from ATP. Fireflies do not have lungs, so they draw oxygen through tubes called tracheoles to turn their lights on and off.
Not all fireflies make light. Some are in an evolutionary rut, still using pheromones — scent — to find mates. Although all fireflies are bioluminescent as larvae, only the most highly evolved fireflies use light as adults, Branham says, and that is the focus of his work.
“A bioluminescent signal system that communicates species identity and can be seen and processed by the receiver of the signal — it’s a pretty complicated thing,” Branham said. “The photic organs in the most evolved fireflies are highly complex.”
The fossil record reveals some of the evolution of light for courtship. When the story begins, fireflies use pheromones, and their eyes are small and antennae large, the better to detect the pheromones of a suitor. More recently, as the photic organ evolves, antennae shrink and eyes enlarge, the better to see the flirtatious male blinking across the meadow.
The fossil record goes back 24 million years, relatively recent in the world of insect evolution, Branham says. Some of the oldest fireflies, captured in Dominican and Baltic amber, show no signs that they used light. Other fossils, Branham says, look like fireflies he collected a few years ago and could even be the same species. Still other fossils show combinations of characteristics he has never seen before in one firefly species. Finding the incremental steps, some things added some subtracted, filling in the evolutionary gaps, fascinates him. It didn’t just happen all at once.
“When I study fossil insects, I feel like I’m back in graduate school and my instructor hands me one of these unknown insects and says, ‘here’s your test; what is this?’”
One of the interesting aspects of bioluminescence is that it has evolved independently multiple times. Although bioluminescence in the ocean is common, on land it’s rare, showing up only three or four times in the insect world over time.
To what end all this flashing? Survival. The warning in the bright coloration of a bee or wasp cannot be seen at night when fireflies are active, so the yellow, green and sometimes blue flashes warn of the presence of defensive lucibufagins in these insects.
Matchmaking, too, relies on bioluminescence, and with only two weeks of life as adults, procreation is serious business. The flash patterns vary species to species. For nocturnal creatures, it’s all about the light. In the singles bar of your back yard, a female will lead several males on at once, but only mate with one. She judges fitness in a flash.
“The only thing a female can see of a male when he’s out flying around is his flash pattern. She can’t assess any other attributes of the male,” Branham says.
Branham questioned whether female preference for particular flash patterns was the cause of speciation. To test the idea, he chose a species that hovers while it flashes. Some fireflies zig and zag and others shake their abdomens, so choosing a species that hovers eliminated movement as a variable. He built a computer-controlled artificial male firefly, programmed signals and transmitted them with a tiny light-emitting diode. He changed the LED to test the effect of light color and intensity on preference and tested flash speeds.
Not only did females like fast flashes, they liked flashes that were far faster than what a male firefly could physiologically produce.
“With my computer-controlled firefly, I could create flashes so fast they were not found in nature, and the females really liked those,” Branham says. “They would flash back much more often, twice as bright, and they would aim their photic organs at the artificial male.”
It was sexual selection at work before his eyes. The results were published in the journal Nature, and Branham is working on a follow-up project to date the actual origin of bioluminescence in beetles.
“Fireflies make a great model for talking about the evolution of complexity in a very non-threatening, very charismatic organism,” Branham says. “Fireflies have such a great story for how you have these added features over time, each one leads to another and another and another and you end up with something very, very complex.”
If Branham needed a reminder of the complexity of the firefly world, he got it when he signed up to help the Smithsonian Institution last year. The Smithsonian owns one of the world’s more important collections of fireflies, or Lampyridae, but has not had anyone to curate it since the 1940s. As one of the few researchers working on firefly systematics and biodiversity, Branham was a logical choice.
Uncurated, the collection had been tucked away in the climate-controlled environs of the Smithsonian, almost a time capsule of the extent of Lampyridae taxonomy circa 1940. Some specimens date back to the late 1800s and have notes written in quill pen, indicating they were sent to Paris for identification by French entomologist Ernest Olivier and sent back.
David Furth, who manages the National Insect Collection with its 35 million specimens, says the firefly collection might have had to be shut down without Branham’s help, and Branham is welcome to work with it until he retires. Improving the collection, Furth says, will make it possible to “ask questions we can’t even think of yet.”
The smell of mothballs lingers, although Branham tossed them out in favor of rotating the cases through ultra-cold temperatures to kill pests that like to eat insect collections. Dozens of cases of fireflies on pins, frozen in time, have gone unnamed and unclassified because the task requires someone who knows the extent to which one specimen is related to another. While 2,000 species are known worldwide, Branham suspects 3,000 more remain to be discovered or named.
While the task ahead is huge — the collection is on a 10-year, renewable loan and will be digitized along the way — the benefit also is huge. The collection provides a great resource for looking at distribution data and diversity within certain groups. The collection will remain active, and researchers who wish to use it are welcomed.
“I can train my students in how to care for a collection, how to make identifications, how to curate and database a large, important research collection, and we don’t have to make trips back and forth to Washington. It’s just right down the hall,” Branham says with the glee of a kid surrounded by birthday gifts.
Furth transferred the specimens to archival containers to absorb vibrations and helped Branham load a moving truck.
“I drove it down here myself,” Branham says, “very carefully.”
Firefly experts from around the world will have another reason to travel to Gainesville in August, when UF hosts the International Firefly Symposium 2014, its first time in the United States. Its most recent venues, in Southeast Asia, made sense Branham says, because fireflies there are an eco-tourist attraction. In Malaysia, mangroves light up at night with so many fireflies that fishermen have used them to steer their boats home.
Although locally the firefly scene is not as spectacular, Florida has more species than any other state in the U.S. and a long tradition of firefly research. UF Professor Emeritus James Lloyd began studying fireflies in the 1960s, and Furth calls him “the granddaddy of fireflies in this part of the world.” Although he retired in 2001, he hasn’t stopped “fireflying.”
Between them, Branham and Lloyd have more than a half-century of working with fireflies and occasionally survey together. Time after time, Branham says, Lloyd tells him a location that used to be prime firefly habitat is gone.
“We’ve seen nights where there’s not a single flash,” Branham says.
Documenting firefly biodiversity, through the ages and today, is important, Branham says, because he suspects there will come a day when biologists will not be able to find them in nature, and instead will have to pull out a drawer in a collection case or open a freezer door to a cryo-collection to see them. Their lights will be out.
Branham says urbanization and all that comes with it — increased pesticide use, loss of habitat, and encroaching lights — is partly to blame. Many sites Lloyd studied are now parking lots and strip malls. Ask average Floridians, Branham says, and they will tell you they don’t often see fireflies, or never have. Part of the reason is timing.
“In Florida, some species are only out for about 23 minutes every night. It’s not 30 minutes, it’s not 20 minutes, it’s 23 minutes,” Branham says.
Even if you turn off the TV or put down your iPad to catch that window of opportunity, you need to be in the right habitat to see them, and that habitat is not likely to be your manicured back yard. Fireflies are out when mosquitoes are out and like moist, natural areas. The same pesticides that kill mosquitoes kill fireflies.
Light pollution, too, is a culprit.
“There are more baseball diamonds, lighted walkways, lights are on all night long much more so than when I was a kid. When there’s all that added light at night, fireflies don’t know when to come out and start signaling,” Branham says. “It just never gets quite dark enough.”
Branham and Lloyd were interviewed for a recent documentary about light pollution and fireflies, “Brilliant Darkness: Hotaru in the Night.” The film is sponsored by the Zoological Lighting Institute, which promotes photobiology and photoecology.
Branham says communities are becoming more sensitive to light as a pollutant that can affect creatures like sea turtles and fireflies and are looking for ways to have a minimal impact on those creatures while still providing safety for humans.
Outreach activities, like the American Museum of Natural History exhibit “Creatures of Light” on which Branham consulted, help educate the public about fireflies. The exhibit, now on a 10-year tour, delves into bioluminescence across the animal world, but fireflies are a big part.
Although Branham and some marine biologists have chatted about a project to assess bioluminescence across animalia, Branham is happy to leave the ocean’s abyss to others.
“With fireflies, you can put 30 of them in a vial and put them in your shirt pocket,” Branham says. “You can’t do that with a big jellyfish.”
Branham says he hopes fireflies can be ambassadors for research into the natural world. He worries that a gulf is growing between the public and nature as people spend more time with technology and less time outdoors.
“The public is not going to see nature as a priority to protect if they don’t have a personal connection to it,” Branham says. “I think that’s where fireflies come in. A firefly is an almost immediate connection between whoever sees it and nature.”
How can an experience so ordinary that millions share it be so extraordinary? Branham’s first firefly memory — and probably yours — is from childhood, playing in the yard at dusk and seeing a flash over the garden.
“To hold a firefly in your fingers and see it flash on and off, it seemed truly magical,” Branham says. “Now, we know how it happens, and it’s even more cool. You’re actually seeing them talk to each other, seeing them court a mate, and it all happens on these dark summer nights.”
Source:
- Marc Branham, Associate Professor, Department of Entomology and Nematology, (352) 273-3915
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This article was originally featured in the Winter 2013 issue of Explore Magazine.